When I left MS, a full Windows build was about 18M LOC. The fact that 18 million lines of code, written by tens of thousands of engineers, worked at all was a mini miracle.
With regard to compensation: like Karpathy, I had already earned enough to be comfortable for the rest of my life. Once money stopped being the primary driver, I was able to focus on what made me happy. Building things, even if you don't like them, brought me happiness and fulfillment. I hope Andrej finds the same at Anthropic.